Photographic developer/amplifier compositions

Abstract: An aqueous redox amplifier composition comprising a colour developing agent, hydrogen peroxide or a compound which provides hydrogen peroxide and hydroxylamine or a salt thereof wherein the concentration ranges are: hydrogen peroxide from 0.5 to 10 ml/l (as 30% w/w solution), hydroxylamine or a salt thereof from 0.25 to 5.5 g/l (as hydroxylamine sulphate), and wherein the pH is in the range from 10.5 to 12.

Description: Field of the Invention This invention relates to photographic developer/amplifier solutions useful in redox amplification processes. Background of the Invention Redox amplification processes have been described, for example in British Specification Nos. 1,268,126, 1,399,481, 1,403,418 and 1,560,572. In such processes colour materials are developed to produce a silver image (which may contain only small amounts of silver) and then treated with a redox amplifying solution (or a combined developer-amplifier) to form a dye image. The developer-amplifier solution contains a colour developing agent and an oxidising agent which will oxidise the colour developing agent in the presence of the silver image which acts as a catalyst. Oxidised colour developer reacts with a colour coupler to form the image dye. The amount of dye formed depends on the time of treatment or the availability of colour coupler and is less dependent on the amount of silver in the image as is the case in conventional colour development processes. Examples of suitable oxidising agents include peroxy compounds including hydrogen peroxide and compounds which provide hydrogen peroxide, eg addition compounds of hydrogen peroxide; cobalt (III) complexes including cobalt hexammine complexes; and periodates. Mixtures of such compounds can also be used. A serious problem with developer/amplifier solutions is their stability because they contain both an oxidising agent (eg the peroxide) and a reducing agent (the colour developing agent) which react together spontaneously thus leading to loss of activity in a matter of an hour or two. In comparison, conventional photographic colour developer solutions suffer loss of activity by aerial oxidation of the colour developing agent. A typical commercial colour developer solution, however, will be stable for a week or two. Both diethylhydroxylamine and hydroxylamine sulphate have been proposed as antioxidants for colour developer solutions. Colour developer solutions for silver chloride colour papers do not contain hydroxylamine sulphate because it can act as a black and white developing agent and this severely inhibits dye yield. Instead, diethylhydroxylamine is used because it does not inhibit dye yield. When using low silver colour papers closely related to currently used silver chloride colour papers to be processed in a redox developer/amplifier it has been found that diethylhydroxylamine works as an effective antioxidant at first but its oxidation products cause a severe loss of hydrogen peroxide after a few hours. Adding hydroxylamine sulphate to a developer/amplifier, as with conventional colour developers, causes dye yield to be seriously inhibited. However, the inventor has found that, unlike the case with conventional colour developers, the inhibiting effect of hydroxylamine sulphate can be overcome by increasing the level of peroxide. Russian specification A-1075227 describes a method for producing a monochrome image by a lengthy process which includes a redox amplification step as step 9 of a 12 step process. The amplifier solution contains both resorcin and hydroxylamine and is shown to be an improvement over using resorcin alone. The solutions contain no alkaline material and it is therefore assumed that their pH values are low. The combination of resorcin and hydroxylamine is said to be essential and thus there is no disclosure that hydroxylamine alone has any utility. The present solutions have a pH of 10.5 - 12 and contain no resorcin. Copending patent application EP-A-0 654 706 of even date herewith describes an amplifier composition comprising a dialkyl substituted hydroxylamine in combination with a colour developing agent and hydrogen peroxide at a pH of 10.5 to 12. Summary of the Invention According the the present invention there is provided an aqueous redox amplifier composition comprising a colour developing agent, hydrogen peroxide or a compound which provides hydrogen peroxide and hydroxylamine or a salt thereof wherein the concentration ranges are: hydrogen peroxide from 0.5 to 15 ml/l (as 30% w/w solution) (molar concentration range 4.4 x 10 -3 - 0.132), hydroxylamine or a salt thereof from 0.25 to 8 g/l (as hydroxylamine sulphate), and wherein the pH is in the range from 10.5 to 12. The concentration range of the hydrogen peroxide is preferably from 0.5 to 10 ml/l (molar concentration range 4.4 x 10 -3 - 0.088), more preferably 0.5 to 7 ml/l (molar concentration range 4.4 x 10 -3 - 0.062) and especially from 0.5 to 2 (as 30% w/w solution) (molar concentration range 4.4 x 10 -3 - 0.018). The concentration range of the hydroxylamine component is preferably from 0.5 to 5.5, more preferably from 0.5 to 4 and especially from 0.5 to 2 g/l (as hydroxylamine sulphate). The pH is preferably buffered by a phosphate. The pH is preferably in the range 11 to 11.7 and especially from 11 to 11.4. The composition is preferably free of any compound that forms a dye on reaction with oxidised colour developer. Advantageous Effect of the Invention The developer/amplifier solution is stabilised against loss of dye yield and as the solution ages peroxide is slowly lost. However, the effect of this loss is compensated for by the concomitant oxidation of hydroxylamine sulphate which, in turn, diminishes its inhibiting effect on peroxide. This effect was entirely unexpected as a similar effect is not observed in conventional colour developers. The stabilised developer/amplifier remains a pale straw colour without forming any deposits. In addition hydroxylamine sulphate is more acceptable to operators who dislike the smell of diethylhydroxylamine. Detailed Description of the Invention The hydroxylamine compound may be hydroxylamine chloride, phosphate or, preferably, sulphate. The phosphate buffer may be potassium hydrogen phosphate (K 2 HPO 4 ) or other phosphates, carbonates, silicates and mixtures thereof. The relative proportions of hydrogen peroxide (as ml/l of a 30%w/w solution) and hydroxylamine compound (as g/l hydroxylamine sulphate) need to be balanced to give the required result. It has been found that the hydrogen peroxide concentration needs to be about twice the hydroxylamine sulphate concentration. Thus the ratio of hydrogen peroxide to hydroxylamine compound is from 1.5 to 2.5, preferably 1.75 to 2.0, ml/l 30% w/w hydrogen peroxide solution: g/l hydroxylamine compound as hydroxyalmine sulphate. The colour photographic material to be processed may be of any type but will preferably contain low amounts of silver halide. Preferred total silver halide coverages are in the range 6 to 300, preferably 10 to 200 mg/m 2 and particularly 10 to 100 mg/m 2 (as silver). The material may comprise the emulsions, sensitisers, couplers, supports, layers, additives, etc. described in Research Disclosure, December 1978, Item 17643, published by Kenneth Mason Publications Ltd, Dudley Annex, 12a North Street, Emsworth, Hants P010 7DQ, U.K. In a preferred embodiment the photographic material to be processed comprises a resin-coated paper support and the emulsion layers comprise more than 80%, preferably more than 90% silver chloride and are more preferably composed of substantially pure silver chloride. The photographic materials can be single colour materials or multicolour materials. Multicolour materials contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the materials, including the layers of the image-forming units, can be arranged in various orders as known in the art. A typical multicolour photographic material comprises a support bearing a yellow dye image-forming unit comprised of at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, and magenta and cyan dye image-forming units comprising at least one green- or red-sensitive silver halide emulsion layer having associated therewith at least one magenta or cyan dye-forming coupler respectively. The material can contain additional layers, such as filter layers. The following Examples are included for a better understanding of the invention. Example 1 - Comparative Example The developer/amplifier(DA1) shown in table 1 uses diethylhydroxylamine as the anti-oxidant at pH 10.3. Developer/amplifier(DA1) Sequestrant 1 0.6g/l Sequestrant 2 2.0ml/l K 2 CO 3 25g/l KBr 1mg/l KCl 0.5g/l Catechol disulphonate (CDS) 0.6g/l Diethylhydroxylamine (DEH) 4.0ml/l CD3 3.5g/l pH 10.3 H 2 O 2 (30%) 5.0ml/l Time 45 seconds Temperature 32°C Where Sequestrant 1 is 60% solution of 1-hydroxy ethylidene-1,1-diphosphonic acid, Sequestrant 2 is a 41% solution of the penta sodium salt of diethylene triamine penta acetic acid and CD3 is N-[2-(4-amino-N-ethyl-m-toluidino)ethyl]-methanesulphonamide sesquisulphate hydrate and DEH is an 85% w/w aqueous solution of diethylhydroxylamine. If this solution is monitored with time while standing at operating temperature in glass measuring cylinders using standard paper control strips then the Dmax falls as shown in table 2. Dmax(x 100) with time(DA1) Time(hrs) R G B 0 282 273 263 1.0 267 259 248 2.0 266 253 236 3.0 257 242 282 5.0 228 208 200 6.0 207 188 176 24 071 097 098 EXAMPLE 2 - Comparative Example The effectiveness of hydroxylamine sulphate as an anti-oxidant depends on the solution pH. If the pH used in DA1 is used with potassium carbonate as the buffer then the peroxide level must be increased considerably from 4ml/l to 14ml/l in order to obtain full amplification. This formula(DA2) is shown in table 3. Developer/amplifier(DA2) Sequestrant 1 0.6g/l Sequestrant 2 2.0ml/l K 2 CO 3 25g/l KBr 1mg/l KCl 0.5g/l CDS 0.3g/l HAS 2.0g/l CD3 3.5g/l pH 10.3 H 2 O 2 (30%) 14.0ml/l Time 45 seconds Temperature 32°C The results of a standing stability test on this formula is shown in table 4. Dmax(x100) with time(DA2) Time(hrs) R G B 0 231 260 230 2 164 219 160 4 111 153 094 6 075 098 095 The standing stability of DA2 is very poor compared with that of DA4 (below) and part of this is almost certainly due to the high peroxide level needed to overcome the inhibiting effect of the hydroxylamine sulphate and obtain satisfactory amplification. EXAMPLE 3 - Comparative Example If the composition of the developer/amplifier shown in table 1 is changed to increase the pH the composition (DA3) shown in table 5 below is obtained. This is changed to a new buffer, phosphate, which controls pH better at pH 11.5 and since activity at this pH is higher the peroxide level is lowered. Developer/amplifier(DA3) Component Concentration Sequestrant 1 0.6g/l Sequestrant 2 2.0ml/l K 2 HPO 4 .3H 2 O 20g/l KBr 1mg/l KCl 0.7g/l CDS 0.3g/l DEH 2.0ml/l CD3 3.5g/l pH 11.5 H 2 O 2 (30%) 1.5ml/l Time 45 seconds Temperature 32°C The standing stability of this formula both with and without diethylhydroxylamine (DEH) is monitored as above. The results shown in table 6 are obtained. Dmax( x 100) with time(DA3) Time(hrs) With DEH (2ml/l) Without DEH R G B R G B 0 274 264 243 272 272 212 1.0 279 269 253 274 270 210 2.5 276 266 252 271 269 208 4.15 279 267 250 273 272 207 5.0 281 269 263 272 270 205 6.0 267 259 255 272 270 202 24 073 097 102 269 267 201 It can be seen from table 6 that up to 6 hours the stability of DA3 with DEH is much better than DA1. After 24 hours both DA1 and DA3 with DEH have essentially become inactive, the densities indicating no amplification. If the DEH is left out of DA3 then the stability is much better with almost full amplification still present after 24 hours. Peroxide analysis with time shows that for DA3 with DEH it falls by about 15% in 6 hours but much more rapidly later. At 24 hours there is no peroxide left. If after 24 hours more peroxide is added then the loss rate is still much higher than a fresh solution. In DA3 without DEH, peroxide loss is about the same over the entire 24 hours. This indicates that although the stability with DEH is quite good for a few hours some product from or caused by DEH accelerates peroxide loss at longer times. This does not happen without DEH. In the absence of an anti-oxidant however the Dmin density is higher because there is no scavenging of oxidised developer in the bulk of the solution and this couples to give an unacceptable Dmin increase. This means that an anti-oxidant is necessary for Dmin control but tends to accelerate peroxide loss. EXAMPLE 4 - Invention If the anti-oxidant DEH in DA3 is replaced by hydroxylamine sulphate (HAS) then very little amplification is observed in the fresh developer/amplifier. This effect is thought to be similar to the effect of hydroxylamine in conventional developers for colour paper based on silver chloride emulsions. Here hydroxylamine acts as a black and white developer and severely reduces the extent of dye formation for a given silver laydown. It has now been found that if the normal level of hydrogen peroxide used in DA3 is increased when hydroxylamine is used as the anti-oxidant then amplification occurs and the fresh sensitometry is restored. This new formula is shown in table 7. Developer/amplifier(DA4) Component Concentration Sequestrant 1 0.6g/l Sequestrant 2 2.0ml/l K 2 HPO 4 .3H 2 O 40g/l KBr 1mg/l KCl 0.5g/l CDS 0.3g/l HAS 2.0g/l CD3 3.5g/l pH 11.5 H 2 O 2 (30%) 4.0ml/l Time 45 seconds Temperature 32°C The results of the standing stability test as used above is shown in table 8. Dmax( x100) with time(DA4) Time(hrs) R G B 0 233 267 253 2 234 265 248 4 241 269 251 6 232 263 244 24 238 262 230 It can be seen from the results that most of the activity present in the fresh developer/amplifier is still present after 24 hours whereas both DA1 and DA2 with DEH show no amplification at all after 24 hours. Example 5 - Invention The level of hydroxylamine is important because the more there is the greater the inhibition of amplification. Several developer/amplifiers based on DA4 were made up with different hydroxylamine levels. In order to obtain correct sensitometry the peroxide level needs to be changed with hydroxylamine level as shown in table 9 below. The standing stability test was carried out on these formulae and the Dmax at the start and after 6 hours and 24 hours is shown in table 9 below. Developer/amplifiers with different HAS levels HAS (g/l) H 2 O 2 (ml/l) Dmax (x100) Start Dmax (x100) 6hrs Dmax (x100) 24hrs R G B R G B R G B 0 0.5 245 255 234 199 216 201 075 097 101 1.0 2.0 252 259 248 256 263 244 261 266 246 2.0 4.0 261 266 250 263 269 254 257 262 230 3.0 5.7 254 264 250 265 264 243 249 265 227 4.0 7.0 255 266 254 252 266 247 240 266 223 It can be seen that the level of peroxide needs to be increased with HAS level in order to maintain sensitometry and that the peroxide/HAS ratio is roughly constant at 2.0 (as a ratio of ml/l of a 30% w/w solution of H 2 O 2 to g/l hydroxylamine as hydroxylamine sulphate). This means that about the same sensitometry can be obtained with different HAS levels provided the peroxide level is changed to match. As well as this less peroxide is needed at lower HAS levels and this shows up in the better standing stability with the lower HAS and peroxide levels. At zero HAS however with the least peroxide the stability is the worst of all. This is different from the result with zero anti-oxidant in table 6 because the level of peroxide in table 6 is too high for good sensitometry. This excess peroxide does not cause much of an increase in fresh sensitometry because for the red and green layers at least the reflection density is already at the reflection limit. This means that any loss in peroxide does not show up as a loss in density and so the system appears to be sensitometrically stable. The blue layer tends to be lower in activity at high peroxide levels and this is reflected in the low Dmax values for the data in table 6. When peroxide loss occurs the competition from the red and green layers decreases and the blue layer benefits. This means that the blue layer does not fall in density as much as it would if the initial peroxide was lower as it was for the data in table 9. Example 6 - Invention In Figure 1 the data for the chemical analysis of DA4 as it ages in the standing stability test is shown. It can be seen that the CD3, hydrogen peroxide and hydroxylamine all slowly lose concentration. It is known that the the loss of peroxide and CD3 lowers activity but the loss of HAS increases activity. The net result of this compensation is that sensitometry falls at a lower rate than for a similar case in the absence of HAS. This with the absence of accelerated peroxide loss with HAS as compared with diethylhydroxylamine as the antioxidant represent the two reasons why HAS allows much more stable redox developer/amplifiers. Example 7 Processing was carried out as before but in a low volume thin tank, as described in copending European Application 0 515 454 or 0 532 558 having a space between parallel major walls of 3mm, over a period of 69 hours. The developer/amplifier had the following formulation: Component Concentration Sequestrant 1 0.6g/l Sequestrant 2 2.0ml/l K 2 HPO 4 .3H 2 O 40g/l KBr 1mg/l KCl 0.5g/l CDS 0.3g/l HAS 1.0g/l KOH (30%) 1.0 ml/l CD3 4.5g/l pH 11.5 H 2 O 2 (30%) 2.0ml/l Time 45 seconds Temperature 35°C The Dmax for the red, green and blue images are recorded below in Table 10. The comparable figures for developer/amplifier DEVELOPER/AMPLIFIER 1 of Example 1 are also shown. Dmax( x100) with time Time(hrs) R G B 0 244 256 246 2 238 257 241 4.5 240 255 239 21.3 241 251 230 28.3 248 255 228 44.5 252 253 226 69.0 261 257 220 Dev/amp DA1 0.5 254 248 222 1.1 251 245 227 3.2 235 228 190 5.5 209 204 169 It can be seen that the comparative developer/amplifier shows a falling off of the Dmax values at 5.5 hours whereas the developer/amplifier of the invention shows very little effect over 69 hours. Example 8 A further processing run was carried as before but in a conventional minilab apparatus. The developer/amplifier had the following composition: Component Concentration Sequestrant 1 0.6g/l Sequestrant 2 2.0ml/l K 2 HPO 4 .3H 2 O 40g/l KBr 1mg/l KCl 0.5g/l CDS 0.3g/l HAS 1.0g/l KOH (50%) 10.0 ml/l CD3 4.5g/l pH 11.4 H 2 O 2 (30%) 2.0ml/l Time 45 seconds Temperature 32°C The results are shown in Table 11 below. Dmax( x100) with time Time(hrs) R G B 0 266 265 263 24 264 263 255 48 267 264 249 72 276 268 254 96 278 272 227 192 223 232 214 216 121 138 149 The results that consistent sensitometric results were obtained over a period of 96 hours while serious deterioration only occurred at 216 hours.

Claims: An aqueous redox amplifier composition comprising a colour developing agent, hydrogen peroxide or a compound which provides hydrogen peroxide and hydroxylamine or a salt thereof wherein the concentration ranges are: hydrogen peroxide from 0.5 to 15 ml/l (as 30% w/w solution) (molar concentration range 4.4 x 10 -3 - 0.132), hydroxylamine or a salt thereof from 0.25 to 8 g/l (as hydroxylamine sulphate), wherein the pH is in the range from 10.5 to 12 and wherein the ratio of hydrogen peroxide to hydroxylamine compound is such as to maintain the required sensitometry. A composition as claimed in claim 1 in which the concentration range of the hydrogen peroxide is from 0.5 to 10 ml/l (as 30% w/w solution) (molar concentration range 4.4 x 10 -3 - 0.088). A composition as claimed in claim 2 in which the concentration range of the hydrogen peroxide is from 0.5 to 7 ml/l (as 30% w/w solution) (molar concentration range 4.4 x 10 -3 - 0.062), A composition as claimed in claim 3 in which the concentration range of the hydrogen peroxide is from 0.5 to 2 ml/l (as 30% w/w solution) (molar concentration range 4.4 x 10 -3 - 0.018). A composition as claimed in any of the preceding claims in which the concentration range of the hydroxylamine component is from 0.5 to 5.5 g/l (as hydroxylamine sulphate). A composition as claimed in claim 5 in which the concentration range of the hydroxylamine component is from 0.5 to 4 g/l (as hydroxylamine sulphate). A composition as claimed in claim 6 in which the concentration range of the hydroxylamine component is from 0.5 to 2 g/l (as hydroxylamine sulphate). A composition as claimed in any of the preceding claims in which the ratio of hydrogen peroxide to hydroxylamine compound is from 1.5 to 2.5 (ml/l 30% w/w hydrogen peroxide solution:g/l hydroxylamine compound as hydroxylamine sulphate). A composition as claimed in claim 8 in which the ratio of hydrogen peroxide to hydroxylamine compound is from 1.75 to 2.0 (ml/l 30% w/w hydrogen peroxide solution:g/l hydroxylamine compound as hydroxylamine sulphate). A composition as claimed in any one of the preceding claims in which the pH is buffered by a phosphate. A composition as claimed in any one of the preceding claims in which the pH is from 11 to 11.7. A composition as claimed in claim 11 in which the pH is from 11 to 11.4.

Inventors: TWIST PETER JEFFERY, TWIST, PETER JEFFERY, TWIST, PETER JEFFERY, C/O KODAK LIMITED
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1994
Main classification: G03C7
IPC codes: G03C7